Events could be caused by cosmic tryst within shared veil of gas

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This image shows the spectacular stellar outburst of V838 Monocerotis in 2002. Scientists now suspect the outburst was caused by a so-called "common-envelope event," an outburst from two stars sharing a gas shell. Image released Jan. 24, 2013.

Scientists have detected what appears to be a stellar outburst from a pair of stars locked in a cosmic tryst within a shared veil of gas, a find that marks the first discovery of a long-sought type of space eruption.

Most outbursts from stars are lumped into two categories — novas or supernovas. A nova is a thermonuclear explosion from a white dwarfstar driven by fuel piled on from a companion star. Novas do not result in the destruction of their stars, but supernovas do.

Supernovas, which are bright enough to briefly outshine all the stars in their galaxies, happen in two known ways — type Ia supernovas occur after a white dwarf dies from gorging on too much fuel from a companion star, while type II supernovas take place after the core of a star runs out of fuel, collapses into an extraordinarily dense nugget in a fraction of a second, and then bounces and blasts outward.

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However, over the years, scientists have recognized another class of outbursts that are brighter than novas but dimmer than supernovas. Investigators called these mysterious events intermediate-luminosity red transients, or ILRTs. [ Top 10 Star Mysteries ]

"I find it extremely exciting that we have explained a class of events that previously no one knew what they were," study lead author Natasha Ivanova, an astrophysicist at the University of Alberta in Canada, told SPACE.com. "That does not happen very often in science."

Two stars in dusty veil
Scientists had long theorized that two stars can temporarily orbit each other with an envelope of gas they share. In these "common-envelope events," the star with less mass should become engulfed by matter from the larger companion star. The interactions between these stars can explosively hurl this super-hot envelope away from them at speeds of up to 2.2 million mph (3.6 million kph), releasing about as much mass as a supernova and about 10,000 times more than a nova.

However, astronomers did not expect to see these events directly. They are both rarer than novas but not as bright as supernovas, making them difficult to spot.

After developing computer models of the properties of common-envelope events, researchers found the energies, colors, short time scales, ejection velocities of ILRTs, as well as the rates at which they happened, match those of the predicted properties of long-sought common-envelope events.

"The surprise was that the appearance of the events (common-envelope events) is very different to what the original predictions were — the outbursts are much brighter and the durations are much longer than once thought," Ivanova said.

New star outburst model
This new model applies best to a subset of ILRTs often called luminous red novae. "It may be expected that not all of the ILRTs must necessarily be caused by common-envelope events, and some don't seem to be easily explained by our model unless it will be extended to take into account further complications," Ivanova said.

Common-envelope events are thought to create many binary systems, and could potentially help produce the progenitors of type Ia supernovas and gamma-ray bursts, the most powerful explosions in the universe. The scientists estimate about 24 common-envelope events happen every 1,000 years per galaxy like the Milky Way.

"We hope that the whole field of studies of interacting binaries — this includes such binaries as Type Ia progenitors, gamma-ray burst progenitors and merging double-stellar black holes — will receive a strong shake up," Ivanova said.

Ivanova and her colleagues detailed their findings in the Jan. 25 issue of the journal Science.

Southern stargazing

Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them.
(Y. Beletsky / ESO)
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A balloon's view

Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich.
(Kyle Moroney / AP)
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Spacemen at work

Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment.
(NASA)
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Special delivery

The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps.
(NASA)
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Accidental art

A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288.
(NASA / ESA)
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Supersonic test flight

A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

Red lagoon

The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes.
(ESO/VPHAS team)
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Fire on the mountain

This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people.
(NASA via AP)
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Where stars are born

An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues.
(NASA / JPL-Caltech)
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A long, long time ago...

This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang.
(NASA / NASA via AFP - Getty Images)
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Frosty halo

Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.